[LLVMdev] seeking a mailing list for llvm ports

[Peter T. Breuer]

"Also sprach Jim Grosbach:"
> out of tree port, you’re in the general right place for LLVM related
> questions, including about the assembler infrastructure.

Great!

> You are correct that the .td files contain most of the information for
> instructions.  All of it for simple instructions, really.  Those files
> are used to create .inc files for asm matchers (it’s a bunch of data
> tables, and a few helper functions) via the tblgen utility.

Aaaaaah. OK. So the .td files are scanned by a woojah and produce .inc
files, which get incorporated in other things (parsers, printers, ...).
Yes, I can see references to the extra instruction I tried defining
coming through in the build dir in the
lib/Target/OR1K/OR1KGenAsmMatcher.inc file.

That's the only place I can see a reference, however. Is that going to
be it?


> The main assembler functionality is in the lib/MC library of llvm,
> with target specific bits in lib/Target/<targetname>/AsmParser.  You can
> start by perusing that code a bit and stepping through the instruction
> matching.  The llvm-mc utility is handy for this, as it’s a developer
> tool that provides a no-frills front end to the assembler and
> disassembler engines.

At the moment that leaves me a bit cold, as I don't know what llvm-mc
is for, hence what I might use it for. The "m" in "mc" sounds like
"meta", so I guess it's a generic engine of some kind. What kind of
input file I might run it on is a mystery to me at the moment, but I
see it has some likely looking options

   -as-lex                 

so I guess it can run over an assembler file. OK, I'll try that. Oooh
.. yes, it does do lexing. I see. I suppose it does more things too,
per option. I'll check to see if I have done enough to get my extra
instruction io

Yes, the lexer is happy. I'll see what else ...

After adding that one more instruction, which is a "prefix" instruction
that allows immediate data for a prefixed instruction to be extended
beyond 16 bits, I would like to change the backend so that

1) it recognizes an extra pseudo assembler instruction that puts it in 
   a special mode, and another that gets it out of it again

2) in the special mode, when it sees an assembler instruction with
   immediate data in, it should emit the machine code for an extra
   prefix instruction before it.

Where would I head over to for those increments?

Regards

PTB